Re: [PATCH v2] Hibernate: check unsafe page should not in e820 reserved region

[Takashi Iwai]

At Mon,  4 Aug 2014 23:23:21 +0800,
Lee, Chun-Yi wrote:
> 
> When the machine doesn't well handle the e820 persistent when hibernate
> resuming, then it may causes page fault when writing image to snapshot
> buffer:
> 
> [   17.929495] BUG: unable to handle kernel paging request at ffff880069d4f000
> [   17.933469] IP: [<ffffffff810a1cf0>] load_image_lzo+0x810/0xe40
> [   17.933469] PGD 2194067 PUD 77ffff067 PMD 2197067 PTE 0
> [   17.933469] Oops: 0002 [#1] SMP
> ...
> 
> The ffff880069d4f000 page is in e820 reserved region of resume boot
> kernel:
> 
> [    0.000000] BIOS-e820: [mem 0x0000000069d4f000-0x0000000069e12fff] reserved
> ...
> [    0.000000] PM: Registered nosave memory: [mem 0x69d4f000-0x69e12fff]
> 
> So snapshot.c mark the pfn to forbidden pages map. But, this
> page is also in the memory bitmap in snapshot image because it's an
> original page used by image kernel, so it will also mark as an
> unsafe(free) page in prepare_image().
> 
> That means the page in e820 when resuming mark as "forbidden" and
> "free", it causes get_buffer() treat it as an allocated unsafe page.
> Then snapshot_write_next() return this page to load_image, load_image
> writing content to this address, but this page didn't really allocated
> . So, we got page fault.
> 
> Although the root cause is from BIOS, I think aggressive check and
> significant message in kernel will better then a page fault for
> issue tracking, especially when serial console unavailable.
> 
> This patch adds code in mark_unsafe_pages() for check does free pages in
> nosave region. If so, then it print message and return fault to stop whole
> S4 resume process:
> 
> [    8.166004] PM: Image loading progress:   0%
> [    8.658717] PM: 0x6796c000 in e820 nosave region: [mem 0x6796c000-0x6796cfff]
> [    8.918737] PM: Read 2511940 kbytes in 1.04 seconds (2415.32 MB/s)
> [    8.926633] PM: Error -14 resuming
> [    8.933534] PM: Failed to load hibernation image, recovering.
> 
> v2:
>  + removed empty check of nosave_regions list.
>  + fixed the typo of "region" in code for error message and patch comment.
> 
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Takashi Iwai <tiwai@xxxxxxx>

Looks good to me, feel free to take my tag,
  Reviewed-by: Takashi Iwai <tiwai@xxxxxxx>


Takashi
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